Mash is also a generic term that people use for feed. Back in the day before pellets were able to be easily made, chicken feed consisted of ground grains that resembled coarse flour. The standard name for that was mash. Very few commercial feeds are in this form today simply because of the huge amount of waste but the term is still out there. Your two standards for laying feed or chick starter today are pellets and crumbles. If they are going from a starter crumble onto a layer feed, I recommend a layer crumble to keep the particle size consistent. Keep them on a starter/grower ration until they are at least 16 weeks or they start to lay.

Mash is a mixture of finely ground grains and other nutrients; finer than 'crumbles'.
A lot of feed mill's sill grind the own mash (starter, grower, and layer) and sell it for a fraction of the commercial name brand feed.